The invention relates to a preform inlet arrangement for an optical fiber drawing furnace, to a furnace provided with that kind of arrangement, and to a preform equipped to co-operate with that arrangement.
The production of optical fibers by drawing a heated preform in a furnace necessarily involves phases during which production is stopped for one preform to be replaced by another.
Stopping a drawing furnace to replace a preform so that the preform to be replaced can be extracted and its replacement installed under good conditions is known in the art. The principal drawback of that solution is that it entails stopping the production of fiber for a relatively long time, for example approximately three hours. This is because it is necessary to return the furnace to production conditions, in particular to the production temperature, before resuming drawing. What is more, the furnace is filled with inert gas during the fiber drawing phase and when replacing one fiber with another the surrounding air can infiltrate into the furnace, which in particular can damage graphite elements inside the furnace which are heated to a high temperature while the furnace is in operation.
A drawing furnace preform inlet arrangement which seals the furnace when a preform is present is known in the art. One example of that kind of arrangement is disclosed in particular in the document DE 4 006 839, which describes a rigid seal surrounding the preform at the top of a furnace lid member through which the preform passes and which is adapted internally for injecting an inert gas around the preform inside the furnace. However, that preform inlet arrangement does not solve the problem of preserving the sealing of the furnace when changing the preform.